The chemical process industry uses a variety of reactors for the production of various chemicals. In many instances the media in which the chemical reactions occur is highly corrosive to conventional metals. In these reactions, high temperatures are often employed in conjunction with aggressive chemical reagents such as acids or alkalis.
As an example, processing or reclaiming precious metals by extraction of the metals from various sources, using methods involving dissolution in aqua regia, is well known. The precious metal group includes silver, gold and platinum. These metals are used in a variety of high performance applications where their outstanding corrosion resistance and catalytic behavior prove useful.
Despite the history of the use of aqua regia and the effort expended in reclaiming the precious metals, severe problems are still encountered due to the difficulty in manipulating and containing this highly corrosive acid, which comprises a 3:1 or 4:1 mixture of hydrochloric and nitric acids, and which will dissolve most metals rapidly. Conventional equipment capable of handling this acid is usually made from ceramics or glass. Problems associated with poor durability and poor shock resistance frequently occur, posing severe safety hazards, and in some cases leading to significant financial losses.
Chemical reactors usually contain various plates, baffles, stirrers, trays, tubes and the like, which are usually made from steel or other metals. In certain chemical reactions, these parts have to be replaced on a frequent basis due to the high level of corrosion that takes place. Replacement of these parts means lengthy reactor downtime with serious economic consequences.
In some chemical reactor applications, graphite has found use due to its corrosion resistance. However, its widespread use is limited by its poor structural properties and overall limited durability.
There is, therefore, a need to develop chemical reactor parts that exhibit superior corrosion resistance compared to conventionally used materials such as steels, and improved structural and lifetime properties compared to graphite. Such materials must exhibit thermal and chemical stability, corrosion resistance, and must not transfer impurities to the products of the reaction, for example, to food additives, catalysts, pharmaceutical compounds and the like.
There is also a need to develop a robust, structural material that is inert to attack by aqua regia. Such a material must be capable of being fabricated into a variety of components. In addition, such a material must be highly pure so that contamination of the high value precious metals is minimized.
High temperature composite materials, in which a ceramic or carbon matrix is reinforced with a continuous fiber, find use in a variety of applications. One common application for composite materials is in aircraft brakes. In this use, the friction, or braking, material is made from a carbon matrix reinforced with carbon fibers (carbon/carbon or C/C). Such materials have high mechanical strength and are capable of operating at extreme temperatures, up to 3000.degree. C. (in a non-oxidizing atmosphere). Composites in which both the reinforcing fiber and the matrix are ceramic find use in specialty applications such as aircraft engine parts where both strength at high temperature and low weight are needed.
Carbon/carbon based composites offer outstanding chemical resistance. This coupled with their lightweight and structural performance makes them ideal candidates for chemical processing equipment. An added advantage is that, according to the present invention, such materials can be produced at extremely high levels of purity, thus minimizing the risks of product contamination.
It is therefore an object of the present invention to provide components for use in chemical process reactors that are superior in mechanical and thermal properties to conventional graphite components.
It is a further object of the present invention to provide components for use in chemical process reactors that are superior in purity characteristics to conventional graphite components and to conventional carbon/carbon materials.
It is a further object of the present invention to provide components for use in chemical process reactors that are superior to conventional metals in corrosion resistance.
It is a further object of the present invention to provide a process for processing or reclaiming precious metals by dissolution in aqua regia, using processing components that are resistant to corrosion by aqua regia.